This invention relates to high energy ignition systems and particularly to a circuit for controlling the starting and ignition of an internal combustion engine while preventing a spark potential from being developed which could otherwise cause untimely ignition in the engine between starting thereof and the normal operating condition.
In mechanical ignition system (points, condensor, etc.) presently employed on many automobiles, the magnitude of charging current through the ignition coil is limited by a ballast resistor to a maximum value. Furthermore, to facilitate engine start up, in response to a start command signal (produced by turning the ignition switch to a start position) a start mode is determined and the ballast resistor short circuited. Subsequently, the charging current is increased during this start mode until it is terminated (release of the start position on the ignition switch). The ballast resistor is then reconnected into the ignition circuit and again limits the current to the maximum value between firing command signals.
However, in contemporary electronic ignition systems no such provisions have been presently made for providing a starting current of greater magnitude than the run mode current. Presently, the magnitude of the current in the start mode is maintained essentially the same as the run mode current. Hence, under some starting conditions, i.e., a weak battery, cold weather, these electronic ignition systems may have poor starting characteristics.
In variable dwell high energy electronic systems now being proposed, it is very desirous to provide a different start current than the normal run current to improve starting of the engine. For example, in such ignition systems where the normal run current is approximately six amps, it is desirous to increase the current during starting to approximately nine amps. Then, after engine starting, the maximum current through the ignition coil would be decreased to the running mode value.
However, another problem occurs in these solid state ignition systems which must be prevented if a higher magnitude of current is generated during the start mode. For instance, as long as the start command signal is terminated in synchronism with the fire command (the discharging of the ignition), no problem is created by the difference in magnitudes of the starting current with respect to the normal running mode current. However, if the start command is terminated, by releasing the ignition switch from the start position, when the current to the coil is in a limited condition, just prior to the next firing command, the instantaneous transition from the start current to the run current, if sufficiently fast, could induce a voltage into the secondary of the ignition coil. If this were to happen, a premature spark could be derived which could cause premature firing in the engine. This spark potential, which acts as an excessive spark retardation, could seriously degrade engine start performance or more seriously, damage the engine.
Thus, there exists a need to prevent premature sparking in the engine due to the transition between start mode and run mode.